A high frequency semiconductor switch having MOSFETs formed on an SOI (Silicon On Insulator) substrate has been utilized in a wireless device such as a cellar phone in order to connect between an antenna and transmitting and receiving circuits.
Recent years, a high frequency semiconductor switch with a multi-port has been developed so as to address widening of a communication frequency band or increase of number of communication standards. Accordingly, an SPnT (Single-Pole n-Throw) switch with one-input and n-output has been used as a frequency semiconductor switch.
The SPnT switch has through FET groups and shunt FET groups. Each of the through FET groups has n pieces of FETs. Each of the through FET groups is connected between an antenna terminal and respective ports. Each of the shunt FET groups is connected between the respective ports and a ground terminal.
Only one of the through FET groups is set in a conductive state and the others are set in a non-conductive state, in the SPnT switch. Thus, the number of through FET groups in an off-state is increased with increase of the number of ports which are provided according to introduction of a multi-port. As a result, the off-capacitance of the SPnT switch is increased so that insertion loss has increasing tendency. A circuit for decreasing off-capacitance and decreasing insertion loss is proposed. In this circuit, decrease of off-capacitance is attained by connecting a common through FET group to one ends of a plurality of through FET groups. However, according to the circuit, when the plurality of the through FET groups are in a non-conductive state, a voltage to be applied between a source and a drain of each FET of the common through FET group becomes high, resulting in increasing distortion current.
Furthermore, the distortion current generated by the off-capacitance is increased in the through FET groups when a voltage applied to the through FET groups in a non-conductive state is high.